<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form method="get" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
    <select name="province">
        <option value="">请选择一个省份:</option>
        <option value="HUNAN">湖南</option>
        <option value="GUANGDONG">广东</option>
    </select>
    <select name="city">
        <option value="">请选择一个城市:</option>
        <option value="CHANGSHA">长沙</option>
        <option value="GUANGZHOU">广州</option>
    </select>
    <input type="submit" value="提交">
</form>
<?php
/********** Begin *********/
if($province = isset($_GET['province'])? $_GET['province'] : '') {
    if($province = isset($_GET['city'])? $_GET['city'] : '') {
        if($_GET['province'] == "湖南" && $_GET('city') == "长沙")
        echo '410000';
        else if($_GET['province'] == "广东" && $_GET('city') == "广州")
        echo '510000';
        else
        echo '选定城市不在选定省份';
    }
}
/********** End *********/
?>
</body>
</html>

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